Prime Minister John Key today signed a tax information exchange agreement with the Cook Islands.
Revenue Minister Peter Dunne said the agreement will enable both countries tax authorities to access each others income and asset information "that would-be evaders try to hide in the other country".
"Having access to that information is especially important at a time when countries everywhere are doing all they can to protect their tax bases."
The recession had prompted international focus on tax co-operation, Mr Dunne said.
New Zealand has similar agreements with the Netherlands Antilles and Bermuda.
Cook Islands Prime Minister Jim Marurai and Mr Key signed the agreement in Rarotonga this morning.
Mr Key is on the final day of his four-day Pacific tour.
The Cook Islands were previously on an OECD blacklist of uncooperative tax havens.
They were removed after pledging to improve its tax and regulatory systems.
